1. Field of the Invention
The present invention relates to wireless data transceivers, and in particular, to asynchronous, full duplex wireless data MODEMs with data encoding and decoding.
2. Description of the Related Art
As modern computer systems have moved away from centralized processing, such as with mainframe computers, toward more distributed processing, such as with personal, or desktop, computers, the need for providing reliable communications between the remote processing elements has become greater. A common conventional communication link has been a data transceiver often referred to as a MODEM (MODulator/DEModulator) in which data is modulated, transmitted over the communication medium, and then demodulated at the receiving end.
Perhaps one of the most common MODEMs is one in which the data is transmitted and received over telephone lines. These types of MODEMs, as well as many other types, rely on a "hard-wired" connection and typically operate in a simplex or half duplex mode. However, hard-wired communication links tend to restrict the mobility of the users. Further, any reconfiguration of the communication link requires the time and expense of relocating, or otherwise reconfiguring, the hard-wired connections, e.g. installing and/or relocating cables.
Accordingly, a solution has been developed which has seen increased use as wireless communications technology advances, namely wireless MODEMs. Such MODEMs continue to transmit and receive data but do so without using wires or cabling as the communication medium. Instead, data transmission is accomplished wirelessly, i.e. "over-the-air" with the atmosphere (or space) as the communication medium. This results in a significant increase in mobility of the users, as well as enhanced opportunities to operate in a full duplex communication mode.
Various types of wireless MODEMs have been proposed. For example, the MODEM described in U.S. Pat. No. 4,759,078 provides for wireless data communication by transmitting data via a "leaky" local oscillator which has been modulated by the data intended to be transmitted, and receiving wireless data via a receive antenna and down-converting it with the aforementioned local oscillator. However, upon closer scrutiny of the proposed MODEM, a number of disadvantages will be realized.
One disadvantage results from the very feature which is expressly intended to be advantageous, namely the use of a "leaky" local oscillator for signal transmission whereby a separate transmit antenna is unnecessary. A problem with this is that it is difficult, if not impossible, to determine just how "leaky" the oscillator must be for reliable signal transmission. Further, by purposely causing the local oscillator to be "leaky", interference with or self-jamming of the companion receiver would be difficult to avoid. Moreover, full duplex operation of this type of transceiver would further suffer from interference with the receive signal due to the presence of modulation on the internal local oscillator.
Further still, such a transceiver design still requires a radio frequency ("RF") interface between the transmitter and receiver sections. In other words, a hard-wired RF interface is needed to convey the local oscillator signal from the transmitter section in which it resides to the receiver section for use therein as the local oscillator for down-conversion of the received signal. Hence, while maintaining a sufficiently "leaky" local oscillator to effect data transmission, it becomes much more critical to provide reliable RF shielding for the receiver, particularly the intermediate frequency ("IF") section, from outside radiation interference.
Therefore, it would be desirable to have a simple wireless data transceiver which would allow for full duplex operation and simple, reliable data modulation and demodulation.